Answer:
[tex](40+2x)\ ft[/tex]
Step-by-step explanation:
we know that
The length of the rectangular swimming pool is equal to
L=40 ft
The square tiles are x feet in length surrounding the pool
so
The longest side of the pool and the tile border is equal to the sum of the length of the swimming pool plus two times the wide of the square tiles
[tex](40+2x)\ ft[/tex]